1. Technical Field
The present invention relates generally to a cooperative cognitive radio (CCR) network and, more particularly, to a spectrum sensing scheme for a CCR network.
2. Description of Related Art
With a rapid increase in demand for radio frequency bands, the value of radio frequency spectrum has increasingly grown. As a technology for increasing the efficiency of the use of radio frequency spectrum, dynamic spectrum assignment-based cognitive radio (CR) has attracted attention as a solution to the problem of lack of radio frequency spectrum.
In a CR system, a primary user (PU) has priority for a specific spectrum band. When the PU does not use the corresponding spectrum band, that is, a PU signal is not present, any secondary user (SU) can communicate in the corresponding spectrum band within a range in which the use of the spectrum of the SU does not interfere with the use of the spectrum of the PU. In order for the CR system to efficiently and flexibly operate, the support of a reliable spectrum sensing technology is essential.
Spectrum sensing technology is divided into coherent, non-coherent and signal feature detection schemes.
In most cases, since a CR does not have sufficient information about a transmission method, a pilot, a coherence message, etc. with respect to a PU signal in a spectrum band to be used, a non-coherent scheme-based spectrum sensing technology is commonly used. For example, energy detection is a non-coherent scheme-based spectrum sensing technology that requires a minimum amount of information about a transmission environment and that has a low level of complexity.
Meanwhile, although a PU has actually occupied a spectrum band, there may be cases where a specific CR uses the corresponding spectrum band because a PU signal is not detected due to fading or shadowing at a location or the time at which the CR is operating. In this case, the PU is subjected to communication interference.
To meet the need for technology for overcoming fading or shadowing, cooperative spectrum sensing (CSS) schemes in which a plurality of CRs achieves spatial diversity by sharing and joining together a plurality of pieces of spectrum sensing information (SSI) have appeared.
In these CSS schemes, each of the SUs transmits SSI indicative of the results of its individual determination of whether a PU signal is present in a spectrum band of interest to a fusion center (FC), and the FC joins a plurality of pieces of SSI together and finally determines whether a PU signal is present.
The above conventional CSS schemes are based on the assumption that noise follows a Gaussian distribution. However, in the practical communication environment, non-Gaussian impulsive noise often occurs due to a moving large object, a power line opening/closing transient phenomenon, the startup of a vehicle, waves reflected from the surface of the sea, lightning, solar winds, or the like. In this case, noise is modeled by an impulsive noise model. Furthermore, SUs may be operating in respective different noise environments.
The conventional Gaussian noise distribution-based CSS schemes are problematic in that they exhibit poor performance in such actual noise environments.